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Elliott Sound Products  DF100 Digital Flash Trigger 

DF100 Digital Camera Slave Flash Trigger

Many of the popular digital cameras used today feature a "pre-flash" which the camera uses to calculate the white balance.  The pre-flash is typically 100ms (100 milliseconds, or 1/10th second) before the main flash, and if you have an investment in your "pre-digital" slave flash units, these are rendered virtually obsolete if your new camera uses pre-flash. Conventional light triggered slave units will not work with any digital camera that uses pre-flash.  All such slave units will fire on the pre-flash and and they cannot cycle quickly enough to fire again when the picture is taken 100 ms later.

For underwater use, most of the "on camera" flash units do not have a sufficient output to illuminate the scene (approx 2/3 reduction in flash effectiveness v distance).  There is another problem - "Backscatter", where the "on board" camera flash illuminates the nearer (out of focus) particulate in the water column between the camera and the subject, this reflects back into the camera and renders the frame useless.  A decidely non-useless frame is shown below to give you an idea of the capability if the system.

Most new housing / strobe manufacturers currently use an optically triggered device for digital cameras, housings using a watertight connector such as the standard Nikonos fittings are rare. The DF100 offers existing photographers who use a film medium and have strobes / slaves that will fire on a single strobe pulse a significant opportunity to protect the investment that they already have ($$$$).

The DF100 module is designed to fire your existing low voltage trigger strobe units on the second flash, when the camera actually takes the photo.  It does this by ignoring the first flash, and only triggering the external strobe on the second flash from the camera. 

Although originally designed for underwater photography, the DF100 is just as useful on dry land, the only difference being the housing required.  Indeed, for use in a studio or other indoor activities, it can be used with no housing at all.

The DF100 module is available as a bare unit that you can install in any housing you choose, in a standard casing, or in a waterproof housing (to 40 metres depth).  In all cases, there is no connector supplied, as the range is too great.  The standard lead supplied is 1 metre of 2-core shielded cable with housed units, and for modules there are 3 pins for attachment of the lead (and an optional battery).

Depending on your flash unit, the DF100 will normally be powered directly from the flash itself, requiring no external power source.  Where the available power is too low, the module can be powered from a 6V camera battery, which will last for almost the shelf life of the battery, provided a suitable cap is placed over the photo sensor.

Note that the unit is polarity sensitive, and will only work with strobe flashes using low voltage triggering (typically 12V or thereabouts).  If it does not work, then simply reverse the polarity of the connection to your strobe.

High voltage triggering (300-400V) is not available at this time, but may be offered if there is sufficient demand.  Connection of the DF100 to a high voltage strobe will damage the circuitry, and any such damage is not covered by any warranty.

The module described is not a kit - it has been completely built and tested, and all major specifications are verified for each unit.


The DF100 is a slave flash synchronisation unit that triggers the external strobe on the second flash from a digital camera.  Should a "stray" flash or burst of light hit the photo sensor, it will automatically reset in approximately 700ms.  This prevents the unit from remaining in an "invalid" state, which would allow it to trigger on the next flash it received (the camera pre-flash).  When the DF100 resets itself, it will trigger the strobe - this is quite normal.

The output of the DF100 is three wires - common, external power (typically +6 to +12V) and a trigger lead.  For many flash units, the power and trigger leads can simply be joined together, and no battery will be required.  Standby current drain is extremely low, so even if a battery is used, a switch is not necessary.

The sensor will not react to normal lighting, but in some cases you may find that it is still too sensitive, and does not allow the strobe flash to operate.  It may be made less sensitive by using an infra-red filter, or a piece of exposed colour slide film.  In many cases, a cardboard shield will be sufficient to shield the DF100 from nearby bright lighting.

DF100 Module
The DF100 Module (Enlarged Image)

In the photo above, the three pins for connection are clearly shown. The upper pin is power, centre pin is the trigger (these will usually be connected together), and the lower pin is ground (negative). The photo sensor may be angled to suit your application when you buy the module by itself.

The DF100 flash trigger units are supplied with full documentation, showing the typical connections required.  Under normal circumstances, a separate battery is not needed, but provision is made for one with the standard leads or the bare module.  Should your flash unit not be able to power the DF100, you will need to use the DF100 with an external battery, or supply your own housing with sufficient space for a battery.

Maximum Ratings and Specifications

Absolute Maximum Ratings ( Note 1)

  1. Absolute ratings refer to values that, if exceeded, may damage or destroy the module.  These ratings must not be exceeded.

Operating Voltage6 to 15V DC only
Maximum strobe output voltage15V DC
Minimum strobe idle current on trigger lead2 uA *
Minimum duration between pre and main flash2 ms
Maximum duration between pre and main flash500 ms
Automatic reset timing600ms (approximately)
Operating range5 metres (typical) in air, 0.5 metre (typical) underwater
Dimensions15 x 40 millimetres (DF100/M) - 15 x 50 mm including sensor

 * Strobes that have less than 2 uA trigger lead current cannot self power the DF100, and an external battery will be required (6-12V)


DF100/MModule only, terminal connections, no housingAU$ 60.00 plus pack and post

The DF100/M is available now, and payment is accepted by credit card (Mastercard, Visa or PayPal).  Please contact ESP if you'd like to purchase one of these units.

The DF100/M is 13mm x 40mm in size, excluding the sensor (an extra 10mm, approximately).  Being so small, it is easy to attach to any camera (with the sensor "viewing" the camera's on-board flash), and may be attached using VelcroTM or similar.

This is a unique product, and to my knowledge there is only one similar unit available.  The competing system does not have the ability to be self powered, is physically very much larger, and is considerably more expensive.  It is also unsuited to underwater photography.

The flexibility of the DF100 is enhanced by your ability to purchase the module without a housing, as this means that by bending the leads to the sensor, it can be tailored to suit the mounting method most appropriate for your needs.  The standard unit is supplied as end-sensitive (i.e. the end of the DF100 faces the camera flash).  With little effort, it can be made side-sensitive, so it can stand upright.  The instructions supplied describe how the sensor can even be removed and attached to a wire (up to 400mm in length) for even greater flexibility.

Limited Warranty

The DF100 (in any form) is unconditionally guaranteed for a period of one year from date of purchase, and will be replaced immediately if it should fail due to faulty materials or workmanship.  Damage caused by water leakage (if you supply your own housing), connection to a high voltage strobe head, or physical damage is not covered.

Full warranty details are supplied with the unit.  The supplied module is warranted to be free of manufacturing defects or other faults in materials or workmanship, including damage sustained in transit from ESP to the purchaser.  Limitations on this warranty are based on the fact that ESP has no control over the final disposition of the unit, or that it has been correctly wired and mounted, and operated in accordance with the supplied instructions.  Units that have been used in excess of any absolute maximum parameter (as detailed above) or have been incorrectly wired (for example to a high voltage trigger circuit) or have been damaged or tampered with are not covered by this warranty.

If used completely within the ratings, the module is covered by a 12 month repair or replacement warranty, provided that it is returned properly packed, and intact and unmodified in any way.  ESP reserves the right to deny warranty claims if it is determined that the fault was caused by excess voltage, tampering of any kind, PCB or component physical damage (other than damage in transit from ESP to the purchaser). 

A repair service is available for units that have been damaged, but it is at the discretion of ESP as to repair an existing unit or replace it completely (depending on the damage sustained).

Example Photo

The photo below was taken using a typical high-end digital camera, and used the DF100 to trigger the external strobe flash.  The image resolution has been reduced for the web, but this gives you an idea of the clarity and sharpness available.

This photo was taken in a small cave just outside Sydney Harbour, at a depth of about 25 metres.  With the camera's on-board flash, this photo would have been unusable, but as you can see, it is anything but!  My thanks to Chris Partridge for the image, which was taken using the production prototype of the DF100 trigger unit.

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Copyright Notice.This article, including but not limited to all text and diagrams, is the intellectual property of Rod Elliott, and is Copyright © 2002.  Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro- mechanical, is strictly prohibited under International Copyright laws.  The author (Rod Elliott) grants the reader the right to use this information for personal use only, and further allows that one (1) copy may be made for reference while constructing the project.  Commercial use is prohibited without express written authorisation from Rod Elliott.
Page Created and Copyright  © Rod Elliott 12 Aug 2002